An airplane is moved by a number of jet engines each housed in a nacelle that also accommodates a set of ancillary actuation devices associated with its operation and handling various functions when the jet engine is operating or stopped. These ancillary actuation devices notably comprise a mechanical thrust reverser actuation system.
A nacelle generally has a tubular structure comprising an air inlet upflow of the jet engine, a mid section designed to surround a fan of the jet engine, a downflow section accommodating thrust reversal means and designed to surround the combustion chamber of the jet engine, and is generally terminated by an exhaust duct, the outlet of which is situated downflow of the jet engine.
Modern nacelles are designed to accommodate a dual-flow jet engine which uses the blades of the rotating fan to generate a flow of hot air (also called primary flow) from the combustion chamber of the jet engine, and a flow of cold air (secondary flow) which circulates outside the jet engine through an annular passage, also called artery, formed between a fairing of the jet engine and an internal wall of the nacelle. The two airflows are ejected from the jet engine through the rear of the nacelle.
The role of a thrust reverser is, when landing an airplane, to improve its braking capacity by redirecting forward at least a portion of the thrust generated by the jet engine. In this phase, the reverser obstructs the cold flow artery and directs the latter towards the front of the nacelle, thereby generating a counter-thrust that is added to the braking of the wheels of the airplane.
The means implemented to produce this reorientation of the cold flow vary according to the type of reverser. However, in all cases, the structure of a reverser comprises moving cowls that can be moved between, on the one hand, a deployed position in which they open, in the nacelle, a passage for the deflected flow, and on the other hand, a retracted position in which they close this passage. These cowls can fulfill a deflection function or simply activate other deflection means.
In the case of a reverser with grilles, also known as a cascade reverser, the reorientation of the airflow is performed by deflecting grilles, the cowl having only a simple sliding function with which to uncover or recover these grilles, the translation of the moving cowl being performed along a longitudinal axis substantially parallel to the axis of the nacelle. Complementary blocking doors, activated by the sliding of the cowling, are generally used to close the artery downflow of the grilles so as to optimize the reorientation of the cold flow.
In addition to its thrust reversal function, the sliding cowl belongs to the rear section and has a downflow side forming an exhaust duct with which to channel the exhaust of the airflows. This duct can complement a primary duct channeling the hot flow and is then called secondary duct.
It is known to address the problems of adapting the section of the duct to the various flight phases encountered, in particular the airplane's take-off and landing phases.
In order to do so, the prior art provides (see FIGS. 1 and 2 of the appended drawing) a thrust reverser comprising, on the one hand, grilles 11 for deflecting at least a portion of an airflow from the jet engine, and on the other hand, at least one cowl 10 that moves translationally in a substantially longitudinal direction of the nacelle able to switch alternately from a closed position in which it ensures the aerodynamic continuity of the nacelle and covers the deflection grilles 11, to an open position in which it opens a passage in the nacelle and uncovers the deflection grilles 11.
The moving cowl 10 comprises an external portion 10a and an internal portion 10b each fitted to move in translation and connected to a telescopic actuating cylinder 30 able to be used to translate them longitudinally (see FIG. 2). The external portion 10a (downflow side of the cowl 10) forms an exhaust duct with which to channel the exhaust of the airflows.
By dividing the moving cowl 10 into an internal portion 10b and an external portion 10a that can be moved at least partially independently of one another, it is possible to adapt the relative positions of the external portion 10a and of the internal portion 10b to the flight conditions so as to vary the section of the exhaust duct formed by the moving cowl 10 by varying the length of the internal aerodynamic line of the moving cowl 10, both when the moving cowl 10 is in the closed position and covering the deflection grilles 11, and when the moving cowl 10 is in the open position.
The telescopic cylinder 30 has a first rod 30b for moving the internal portion 10b and a second rod 30a fitted to slide in the first rod 30b to move the external portion 10a of the cowl. The internal portion 10b is attached to the first rod 30b via oblong eyelets 32 arranged either side of the rod 30b, so as to reduce the overhang of the attachment point and avoid any hyperstaticity in the alignment of the three points of attachment of the cylinder 30 to the stationary front frame and to the external 10a and internal 10b portions of the moving cowl.
This solution is satisfactory for a pneumatic or hydraulic cylinder which has sufficient available power to compensate the occurrence of spurious friction forces between the two cylinder rods 30a and 30b, due to incorrect alignment.
On the other hand, for an electric cylinder, spurious friction forces are still damaging because the need to increase the available power to overcome these frictions is then deflected in an overdimensioning of the electric motor controlling this cylinder, which affects the weight, the bulk and therefore the cost of the assembly.
Moreover, a dual-acting electric cylinder generally presents actuation difficulties. In practice, since the second rod moves relative to the base of the cylinder, it is difficult to regroup the actuation means in said base of the cylinder and the second rod must generally be fitted with its own motor, which will therefore also move.